Antennas are old and well-known devices in the art that have seen a wide array of manifestations. Antennas may be optimized for use on a single radio frequency, designed with several conductors optimized for multiple frequencies, or designed to harmonically resonate at multiple frequencies. Harmonically operated antennas are somewhat compromised in that not all harmonics (especially the fundamental) are related by an integer (i.e. "perfect" octave or octaves) due to end effect. Thus, expensive antenna tuning devices are often additionally required to provide a low standing wave ratio to the transmitter on some frequencies. A more reasonable approach is an inexpensive antenna that is capable of resonating on multiple frequencies, and which utilizes traps to electrically lengthen or shorten the antenna and selectively alter the fundamental frequency and the harmonic frequencies.
A patentability investigation was conducted and the following U.S. Pat. Nos. were found: U.S. Pat. No. 2,967,300 to Haughawout; U.S. Pat. No. 3,339,205 to Smitka; U.S. Pat. No. 4,062,017 to Thompson; and U.S. Pat. No. 4,423,423 to Bush.
The U.S. Pat. No. 2.967,300 to Haughawout teaches a multiple band antenna utilizing a half wave dipole radiator comprising two like sections, each including three coaxial or concentric elements of graduated length. Each of the sections includes telescoping tuning sleeves between two of the radiating elements. Parasitic elements, for increasing directivity, also include coaxial and parasitic elements.
The U.S. Pat. No. 3,339,205 to Smitka teaches an array of antennae in which the motion or resonance of an individual dipole is simulated by successive connection of the interconnected dipoles. The dipoles are of a length in which the natural wavelengths of the dipoles are far outside the operational frequency to minimize parasitic interaction of passive antennae. The array of dipoles are switched in and out of the antenna circuit by means of diodes and control pulses. This antenna is typically used in Doppler navigation systems for receiving.
The U.S. Pat. No. 4,062,017 to Thompson discloses a multiple frequency antenna formed of a plurality of conductors interconnected by coaxial cable and connected to a feedline or transmission line. This antenna uses several radiating elements in covering multiple bandwidths.
The U.S. Pat. No. 4,423,423 to Bush teaches a folded dipole antenna for use over a broad bandwidth which has a shortened overall length proportional to the operational bandwidth. The folded portions of the dipoles are set apart by spacer members.
None of the foregoing prior art U.S. Patents teach or suggest the particular apparatus or method for the antenna of the present invention. More particularly, none of the foregoing prior art teach or suggest the antenna of the present invention which is an inexpensive multiple frequency harmonic antenna that is capable of transmitting and receiving wide bandwidths with a low standing wave ratio. The antenna of the present invention can be used on most sets of harmonic frequencies and is an excellent candidate for use on Radio Amateur High Frequency Bands, or commercial and/or military operations especially when using frequency-hopping, band hopping and/or other spread-spectrum modulations.